An electric energy storage device, for example a battery, in particular a high-voltage battery, can be provided in a motor vehicle for operating an electric drive motor. High voltage here is to be understood as an electrical voltage of more than 60 volts, in particular more than 100 volts. For charging the energy storage device, a charging cable of a charging station external to the vehicle can be connected to a charging receptacle or charging socket of the motor vehicle. During charging of the energy storage device, a heating of a component of the charging socket can occur. Protection against an overheating must be provided here.
The temperature in the charging socket is measured currently via a temperature sensor. The charger is the component that connects the charging socket to the energy storage device and that controls the charging current. When a temperature that lies above a threshold value is indicated by the temperature sensor, the charging process is interrupted in order to protect the charging socket and the charging plug of the charging cable. Since the temperature sensor is found, in fact, in the charging socket, but does not have direct contact with the phase contacts, the temperature value signaled by the temperature sensor does not involve the actual temperature at the hottest point (English: hot spot) of the charging socket, but rather is an orienting value, which must be effectively interpreted as correct so that one reliably recognizes an over-temperature in the charging socket itself.
This interpretation is effectively difficult, since charging sockets of many different variants are used. There are different power classes, which are distinguished with respect to the electrically conductive cross section of the components of the charging socket. There are also different versions for different countries and these define a geometric configuration of the charging socket. Also, a plurality of different plugs of charging cables can be connected to a specific charging socket, so there are also many plug combinations. Different positions for the temperature sensor in the structure of the charging socket are also possible.
These differences mean that there is a broad temperature range for a necessary disconnection in order to protect the charging socket. In other words, the threshold value with which the temperature value signaled by the temperature sensor is compared must be adjusted relatively low in order to reliably prevent overheating for all conceivable operating configurations in which the charging socket can be operated. The functional range is limited thereby, however, since there are a number of combinations in which the threshold value is too low. In other words, potential that involves the transmission of electrical power for a rapid charging of the energy storage device is wasted here.
A method for operating a charging port apparatus for electric vehicles is known from WO 2013/152376 A2. Exceeding the admissible current carrying capacity of a charging cable is avoided with the method. For this, the root mean square value of the current that thermally loads the charging cable is determined on the basis of a current measurement.
A modular system for a charging device in which a temperature sensor is also integrated is known from DE 10 2012 019 605 A1. By monitoring the temperature, it is assumed that a temperature which increases to above a specific value can supply an indication of an error function, whereas it is assumed that a temperature within the region defined by limit values signals that a charging process is correctly proceeding.
A plug connector for an electric vehicle in which a current measuring device and a voltage measuring device are integrated for measuring a charging voltage is described in DE 10 2010 045 131 A1.